Television tube



July 8, 1941; scHLESlNGER 2,248,558

TELEVISION TUBE Filed July 23, 1958 Patented July 8, 1941 TELEVISION TUBE Kurt Schlesinger, Berlin, Germany, assignor, by mesne assignments, to Loewe Radio, Inc., a corporation of New York Application July 23, 1938, Serial No. 220,875 In Germany October 22, 1937 Claims.

It is known that high-quality television tubes are constructed to advantage when a cathode ray, which emanates from a relatively large-surface cathode, is preliminarily concentrated on to a diaphragm having a narrow aperture, and that this diaphragm is then reproduced by an electronoptical lens on the luminous screen. It is only in this way that a constant diameter of the image or focal point can be ensured in the case of variable intensity of the ray current. The principal difiiculty resides in the carrying out of the preliminary concentration of an electronic bundle of large cross-section on to a diaphragm having an aperture as small as possible for the purpose of avoiding considerable ray current losses. The difficulty is increased if the intensity control of the bundle is to take place prior to the entry into the preliminary concentration system (VK system), which is the ease in all arrangements having a grid in front of the surface of the cathode. These grid controls represent themselves under certain conditions, which are usually fulfilled, as variable lenses, and accordingly take effect on the angle at which the electronic rays enter the VK system. A further problem, which actually is very similar to the question of a powerful optical system for a cinematograph projector, resides in the manner in which the electronic rays emerging from the diaphragm, which exhibit a considerable divergence, are to be collected on to the objective disposed at a remote point to the rear. In magnetic lenses, and more particularly in long magnet coils, this difiiculty can be avoided more readily than in the case of thin electrostatic lenses. The difiiculty is all the greater the smaller the lens aperture may be. The latter in turn must be particularly small if the electrostatic plate defiection is to be built into the tube. Lenses which co-operate with deflecting plates can hardly have a larger diameter than 1 cm.

The present invention is concerned with means for avoiding the above stated diificulties occurring in the design of tubes having an intermediate diaphragm which surrounds a first cross-over point of the ray and the aperture of which, at the same time, acts as the object of the electronoptical reproduction.

The invention will be better understood with the aid of and the essential features of the invention will be apparent from the following more detailed description and the accompanying drawing of which in a purely diagrammatic fashion and by way of example- Fig. 1 shows the electrode configuration of the electron-optical systems for producing controlling, focusing and deflecting the cathode ray,

Fig. 2 shows a preferred embodiment of the electrode system of Fig. 1, illustrating means for securing the position of the electrodes with respect to one another.

The television tube according to the invention is characterised by the following special features: (1) Thick grid. By means of a perforated grid I (Fig. 1) which is comparatively long in the direction of the ray, the penetration of the field of the first suctional anode 2 to the cathode 3 is reduced to a considerable extent. The equipotential surfaces are already substantially parallel to the cathode at the cathode end of the grid. The control of the cathode accordingly takes place over the complete surface, With which there is associated a considerable increase in the slope of the control characteristic. On the other hand the outlet angle depends only to little extent on the biased condition of the grid, so that constant conditions associated with the entry of the ray into the VK system 2, 4, 5 are to be expected.

(2) No immersion lens between grid and cathode. Owing to this eifect according to the invention, brought about by potentials of more than 300 volts in conjunction with the long grid according to (1), the immersion effect, i. e. the preliminary concentration of the rays upon leaving the cathode, disappears. The latter is in the form of a flat cathode with large oxidation surface 3a, not a recessed cathode. The whole system behaves over the entire control characteristic as if the electrons were emitted along parallel lines perpendicularly to the surface of the cathode (bundle of rays Ea) Only the density of the ray current is controlled.

(3) Low-voltage diaphragm. The diaphragm 1 is raised to the same potential as the first anode. The preliminary concentration system consists of a condensing lens. This is made up of a cylinder 4 connected with the cathode, in conjunction with two annular discs 2 and 5 raised to the preliminary anode potential 8. The focal distance of this system is so adjusted by selection of the width of aperture and the length of this cylinder (Z/ 1' adjustment) that the electrons, after leaving the condensing lens, have in a certain defined position a point of intersection 61). At this point of intersection there is located the diaphragm 1. According to the invention, it is raised to the same potential as the inlet and outlet members of the preliminary concentration lens. The advantage obtained by the fact that the diaphragm is raised'to a comparatively low potential is well known. It resides in utilisation of the reducing effect of an electron acceleration ratio) taking place later. In this way, with prescribed. diameter of the image point, the aperture in the diaphragm can be selected to be correspondingly larger. Accordingly, losses are again avoided.

In the l/r adjustment of the cylinder 6 attention should be paid to the fact that when increasing its length there is an increase in the refractive power, but that for obtaining a sufficiently strong refractive power the cylinder may not be extended as desired, as, in the case of a certain extreme length of the cylinder i, which is raised to cathode potential, the electrons cornmence to undergo reflection in the direction towards the cathode. It is necessary to remain below this limit and to obtain additional increase in the refractive power by the reduction of r until the desired refractive effect takes place upon connection of the cylinder t with the cathode.

(4) Diaphragm immersion and secondary electron rejection. Ihe difficulty in collecting the greatly diverging rays 60, after leaving the diaphragm, on to the main objective 9/10 is solved by the provision of a condensing ring immediately following on the object diaphragm, at which ring an adjustment corresponding to the described Z/r adjustment is carried out in the form of suitable selection of the diameter of the opening. A disc H, which is furnished with an opening and with correct selection of the a diameter of the opening can be connected with the cathode, fulfils simultaneously two functions:

(a) It concentrates, particularly in co-operation with the projectory part of the guide cylinder surrounding the diaphragm I, the rays to,

which leave the diaphragm, into a more axialparallel direction 601, and accordingly acts as first weak lens of the reproducing system (diaphragm immersion). The rays are thus concentrated on to the centre of the main reproducing lens 9, whereby losses and marginal errors of the lens are avoided.

(b) The diaphragm immersion II also solves the problem of retaining or collecting the numerous interfering secondary electrons (S. E.) resulting at the object diaphragm I. It has been found that the halo of secondary electrons disposed about the diaphragm reproduction is quickly caused to disappear by a rejector diaphragm H of this nature. The diaphragm H is accordingly preferably referred to as a secondary electron rejector.

The rejection of the secondary electrons, of the two effects (a) and (22), occurs first when the potential of a metal sheet located in front of the object diaphragm is made more negative in relation to the object diaphragm potential, and remains at least upheld as the refractive power of the lens produced by means of the sheet increases. The two adjustments under a and b can accordingly be combined.

The reproducing element located behind these arrangements is of the usual kind. There is concerned a corrected electrostatic lens of small expanse, already described on a previous occasion, between the electrodes 9 and if), the tubular member 53 being in direct electrical connection with the inlet electrode 9 of the lens. The curvature of its field by reason of the secondary electron rejector diaphragm H causes the oospacing from the anode currence of a weak lens effect at l4, which augments the described diaphragm immersion lens in advantageous fashion.

Details of construction: In addition to the advantage of automatic reduction of the scale by a low-voltage diaphragm there is obtained, in considering the numerous electrodes 2, 5, I raised to the same potential 8, the advantage in construction consisting in the fact that all of these diaphragms can be introduced into a common surrounding metal cylinder (1. e. including the object diaphragm l furnished with a particularly narrow aperture). This advantage is very considerable in practice, as heretofore the design of tubes with aperture reproduction has been confronted in practice by a considerable proportion of waste, since obviously it is eX- tremely difficult to direct a ray of /2 mm. in size exactly centrally through a correspondingly narrow aperture. The structural embodiment of a tube according to the invention, in which all measures are combined, is accordingly again shown in Fig. 2. By the inclusion of porcelain rings mechanical fixing and centering together with electrical insulation are conveniently combined. A noteworthy feature is the design of the complete diaphragm optical system, comprising the first anode 2, the condensing cylinder 4, the second anode 5, the diaphragm l, the aperture of which is reproduced, the projectory part of the guide cylinder Ila, which together with the diaphragm H acts as immersion lens, in a common metal tube ll together with the hot cathode 3 and the thimble-like grid element I centered thereon. A system of this kind merely requires to be fitted together and it is already centered and insulated. By means of a porcelain ring IS the low-potential cylinder II can be centered and secured in the medium-potential tube l3.

By means of a further porcelain ring [9 the anode id is placed over the medium-potential cylinder i3, whereby there is formed the centered lens 9/10. Insulating tubes 26 on the one hand provide the deflecting plates 2! with the desired l0 and on the other hand they act as leading-through insulators for the plate deflecting potential through the anode potential. The anode ring I0, by the external application of springs 22, can also be furnished at the same time with an elastic connection with the glass wall of the tube. According to the invention, the porcelain parts are so arranged that they are not to be seen from the ray, i. e. are covered from sight at all points against the zone of the ray by metallic parts. Viewed from the ray, therefore, they are arranged behind the diaphragms or cylinders. This measure is arrived at in the following manner:

In the tubes constructed in the manner set forth uncontrollable interferences with the electron-opticalreproduction were found to occur. Careful investigations showed that these interferences were apparently due to the effect of charges produced on the guide insulators. It was in point of fact found that when the insulators were covered off against the ray by metallic parts the interferences disappeared.

According to an additional feature of the invention, the diaphragm electrodes are produced asfollows: At first there is bored the aperture for the passage of the ray. By means of the ray aperture the sheets are then mounted on a shaft and set into rotation about this shaft and their edge is turned. In this way it is accomplished that the openings in the electrodes are disposed.

exactly centrally in relation to their outer confinements. If then the electrodes are introduced into common cylindrical elements, an exact relative positioning of the electrode apertures is accordingly ensured.

I claim:

1. In a cathode ray tube including a target electrode and wherein a cathode ray is concentrated to a focal point at the target electrode comprising a substantially planar source of electrons, said source having an area at least as large as the cross sectional area of the cathode ray at the focal point, an apertured control diaphragm mounted immediately in front of said electron source, and a pre-concentrating system adapted to focus said cathode ray in a first cross-over point including three annular diaphragms, means for positioning said diaphragms in axial alignment with and displaced along the cathode ray beam from said control diaphragm, and a cylindrical electrode mounted between the two diaphragms most adjacent said control diaphragm, said three diaphragms being directly connected with one another and adapted to be maintained at a positive potential with respect to the potential of said source of electrons, the diaphragm most remote from said control diaphragm being positioned at the beam cross-over point and closely surrounding the beam at that point.

2. In a cathode ray tube as defined in claim 1, wherein said cylindrical electrode is directly electrically connected to said source of electrons.

3. In a cathode ray tube as defined in claim 1,

wherein said three diaphragms are directly connected with one another by a metallic cylindrical element surrounding said diaphragms, said cylindrical element having a diameter greater than the diameter of said cylindrical electrode, the axis of the cylindrical element and the axis of the cylindrical electrode coinciding with the axis of the cathode ray.

4. In a cathode ray tube as defined in claim 1, wherein the aperture in said control diaphragm is circular and has an area substantially identical to the area of the source of electrons, the thickness of the control diaphragm being comparable to the diameter of the aperture therein.

5. In a cathode ray tube as defined in claim wherein said three diaphragms are directly connected with one another by a metallic cylindrical element surrounding said diaphragms, said cylindrical element having a diameter greater than the diameter of said cylindrical electrode, the axis of the cylindrical element and the axis of the cylindrical electrode coinciding with the axis of the cathode ray, a further diaphragm, a further cylindrical electrode and an anode diaphragm, means for positioning said further diaphragm, said further cylindrical electrode and said anode diaphragm along the cathode ray in the order named from said cylindrical element and coaxially with respect to the cathode ray, and means for maintaining said further diaphragm at a potential different from the potentials of the next adjacent cylindrical element and further cylindrical electrode.

KURT SCHLESINGER. 

